JP2013005682A - Non-contact power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-contact power transmission system that can have a simplified configuration, while enabling a heating detection of a metallic foreign body when performing a non-contact power transmission.SOLUTION: In this non-contact power transmission system, an alternating power supplied to a primary coil L1 is received via a secondary coil L2 owing to interlinkage of alternate magnetic flux generated from the primary coil L1 through alternate power supply and the secondary coil L2. The transmitted electric power thus received is supplied to a secondary battery 10. In this system, a temperature detection sheet 30 on which filamentous thermistors are arranged in a grid is attached on the upper surface of the primary coil L1. This temperature detection sheet 30 detects an abnormal heating of the sheet 30 on the basis of temperature detected via the filamentous thermistors. When an abnormal heating of the temperature detection sheet 30 is detected, the alternating power supplied to the primary coil L1 is switched off.

Description

  The present invention relates to a non-contact power transmission system that performs non-contact power transmission between devices using electromagnetic induction.

  2. Description of the Related Art Conventionally, there is known a non-contact power transmission system that charges a secondary battery (battery) for power supply built in an electronic device such as a digital camera or a personal computer in a non-contact manner. In this system, a primary coil and a secondary coil are provided in an electronic device and a dedicated charger corresponding thereto, respectively. For example, when an electronic device is placed on the charger, alternating power is transmitted from the charger to the electronic device through electromagnetic induction between the two coils, and this is converted into DC power by the electronic device. Charging is performed.

  On the other hand, in such a non-contact power transmission system, when a metal foreign object is interposed between the primary coil and the secondary coil, an alternating magnetic flux generated from the primary coil is applied to the metal foreign object. An eddy current is induced in the metal foreign matter to generate Joule heat. For this reason, there exists concern that the housing of a charger or an electronic device may deform | transform by the heat | fever of a metal foreign material.

  Therefore, for example, in Patent Documents 1 and 2, temperature sensors are respectively arranged at a plurality of measurement points set around the primary coil. When any of the temperatures at the plurality of measurement points detected through each temperature sensor indicates a predetermined temperature or more, a metal foreign object is interposed between the primary coil and the secondary coil. Therefore, the power transmission by the charger is stopped. Thereby, since heat_generation | fever of a metal foreign material can be suppressed, the thermal deformation of a charger and an electronic device can be avoided exactly.

JP 2004-208383 A JP 2010-288429 A

  By the way, when the temperature is detected at a plurality of measurement points set around the primary coil as in the non-contact power transmission systems described in Patent Documents 1 and 2, when a temperature is to be detected at a plurality of measurement points, a wide detection range is to be secured. The number of measurement points will naturally increase. And since the number of temperature sensors also increases with the increase in a measurement point, there exists a possibility that the structure of the whole temperature detection part comprised with a temperature sensor etc. may become complicated. That is, there is still room for improvement in simplifying the configuration of the non-contact power transmission system.

  The present invention has been made in view of such circumstances, and its purpose is to enable the simplification of the configuration while enabling detection of heat generation of a metallic foreign object when performing non-contact power transmission. It is to provide a contact power transmission system.

  In order to solve the above-mentioned problems, the present invention relates to alternating power supplied to the primary coil by linking the alternating magnetic flux generated from the primary coil to the secondary coil by supplying alternating power to the secondary coil. A non-contact power transmission system that receives the received power through a load and supplies the received received power to a load, the temperature detecting element being arranged between the primary coil and the secondary coil and extending linearly A temperature detecting unit provided, an abnormality detecting unit provided in the temperature detecting unit and detecting abnormal heating of the temperature detecting unit based on a temperature detected through the temperature detecting element, and the abnormality detecting unit through the abnormality detecting unit The gist of the present invention is to provide power transmission control means for stopping the supply of alternating power to the primary coil based on detection of abnormal heating of the temperature detection unit.

In this non-contact power transmission system, it is preferable that the temperature detection unit is formed in a sheet shape.
In this non-contact power transmission system, it is preferable that the temperature detection elements are arranged in a lattice pattern in the temperature detection unit.

  In this non-contact power transmission system, the temperature detection unit is provided with a power reception coil interlinked with the alternating magnetic flux generated from the primary coil, and the temperature detection unit is connected to the power reception coil by the interlinkage of the alternating magnetic flux. It is preferable to use the induced alternating power as a power source.

In this non-contact power transmission system, it is preferable that the temperature detection unit is provided in the primary coil.
In this non-contact power transmission system, it is preferable that the temperature detection unit is provided on the surface of the housing that covers the outer periphery of the primary coil.

In this non-contact power transmission system, it is preferable that the temperature detection unit is provided in the secondary coil.
In this non-contact power transmission system, it is preferable that the temperature detection unit is provided on the surface of the housing that covers the outer periphery of the secondary coil.

In this non-contact power transmission system, it is preferable that the abnormality detection unit is connected to the power transmission control unit so as to be capable of wireless communication.
In this non-contact power transmission system, the temperature detection unit includes a magnetic coupling coil that is magnetically coupled to the primary coil, and a switching element that short-circuits both ends of the magnetic coupling coil, and the abnormality detection unit includes the abnormality detection unit, When detecting abnormal heating of the temperature detection unit, the amplitude of the alternating power generated in the primary coil is changed by short-circuiting both ends of the magnetic coupling coil through the switching element, and the power transmission control means It is preferable to detect abnormal heating of the temperature detector based on a change in the amplitude of alternating power generated in the coil.

  In the non-contact power transmission system, a wireless communication unit capable of performing wireless communication with the power transmission control unit is provided in a device equipped with the secondary coil, and the abnormality detection unit communicates with the wireless communication unit. It is preferable that when abnormally heated by the temperature detection unit is detected, the fact is wirelessly transmitted to the power transmission control unit via the wireless communication unit.

In this non-contact power transmission system, it is preferable that the abnormality detection unit is connected to the wireless communication unit so as to be capable of wireless communication.
In this non-contact power transmission system, the temperature detection unit is provided with a magnetic coupling coil coupled to the secondary coil, and a switching element that short-circuits both ends of the magnetic coupling coil, and the abnormality detection unit includes the temperature detection unit. When detecting abnormal heating of the detection unit, the amplitude of the alternating power generated in the secondary coil is changed by short-circuiting both ends of the magnetic coupling coil through the switching element, and the power transmission control means It is preferable to detect abnormal heating of the temperature detection unit based on a change in the amplitude of the alternating power generated at the same time.

  According to the non-contact power transmission system according to the present invention, when performing power transmission in a non-contact manner, the configuration can be simplified while the heat generation of the metal foreign object can be detected.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows the schematic structure about 1st Embodiment of the non-contact electric power transmission system concerning this invention. The perspective view which shows the perspective structure of the temperature detection sheet | seat which comprises the non-contact electric power transmission system of the said 1st Embodiment. The circuit diagram which shows the system configuration | structure about the non-contact electric power transmission system of the said 1st Embodiment. The graph which shows the relationship between the temperature of a linear thermistor, and the electric potential of the terminal provided in the sensor control part about the non-contact electric power transmission system of the said 1st Embodiment. The flowchart which shows the procedure of the abnormality detection process by the non-contact electric power transmission system of the said 1st Embodiment. Sectional drawing which shows the schematic structure about 2nd Embodiment of the non-contact electric power transmission system concerning this invention. The circuit diagram which shows the system configuration | structure about the non-contact electric power transmission system of the said 2nd Embodiment. (A) is a time chart which shows the example of switching on / off of a switching element about the non-contact electric power transmission system of the said 2nd Embodiment. (B) is a time chart showing a transition example of alternating power (voltage) induced in the secondary coil. (C) is a time chart showing a transition example of alternating power (voltage) induced in the primary coil. (D) is a time chart showing a transition example of a DC voltage that is rectified by the voltage induced in the primary coil and taken into the primary side control unit. The perspective view which shows the perspective structure of the temperature detection sheet | seat which comprises the system about 3rd Embodiment of the non-contact electric power transmission system concerning this invention. The circuit diagram which shows the structure of the temperature detection sheet | seat which comprises the non-contact electric power transmission system of the said 3rd Embodiment. The circuit diagram which shows the structure of the temperature detection sheet | seat which comprises the system about 4th Embodiment of the non-contact electric power transmission system concerning this invention. The circuit diagram which shows the structure of the charger and portable apparatus which comprise the non-contact electric power transmission system of the said 4th Embodiment. Sectional drawing which shows the schematic structure about 5th Embodiment of the non-contact electric power transmission system concerning this invention. The perspective view which shows the perspective structure of the temperature detection sheet | seat which comprises the non-contact electric power transmission system of the said 5th Embodiment. The circuit diagram which shows the structure of the temperature detection sheet | seat which comprises the non-contact electric power transmission system of the said 5th Embodiment. (A) is a time chart which shows the transition example of the alternating power (voltage) induced by the secondary coil about the non-contact electric power transmission system of the said 5th Embodiment. (B) is a time chart showing a transition example of alternating power (voltage) induced in the primary coil. (C) is a time chart showing an example of switching on / off of the switching element. The circuit diagram which shows the structure of the charger and portable apparatus which comprise the non-contact electric power transmission system of the said 5th Embodiment. The perspective view which shows the perspective structure of the temperature detection sheet | seat which comprises the system about the other example of the non-contact electric power transmission system concerning this invention.

<First Embodiment>
Hereinafter, a first embodiment of a non-contact power transmission system according to the present invention will be described with reference to FIGS. First, a schematic configuration of a contactless power transmission system according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, this non-contact power transmission system includes a portable device 1 such as a digital camera or a notebook personal computer provided with a secondary battery 10 as a power source (load), and a secondary battery 10 of the portable device 1. And a charger 2 for supplying electric power in a non-contact manner.

  The charger 2 includes a primary coil module 20 that transmits power to the mobile device 1. In addition, the charger 2 has a structure in which various electronic components including the primary coil module 20 are covered with a housing 21 to protect them from the external environment. The upper surface 21a of the housing 21 is a portion where the portable device 1 is placed.

  The primary coil module 20 includes a primary coil L1 that generates magnetic flux when power is supplied, and a magnetic body M1 that is made of a ferrite-based member that suppresses leakage of magnetic flux from the primary coil L1. As the primary coil L1, a planar coil in which a conducting wire is wound in the planar direction is used. In the present embodiment, the number of turns of the primary coil L1 is set to 20 turns, and the outer diameter is set to 40 [mm]. The total thickness of the primary coil L1 and the magnetic body M1 is about 1 [mm]. And the temperature detection sheet 30 which detects the temperature of the periphery is affixed on the end surface on the opposite side to the end surface with which the magnetic body M1 of the primary coil L1 contact | abuts with the adhesive agent.

  As shown in FIG. 2, the temperature detection sheet 30 is a sheet-like member made of a polymer film such as PET (polyethylene terephthalate) resin, for example, and linear thermistors SH1 to SH5, SV1 to SV5 are provided therein. Are patterned in a lattice pattern. The linear thermistors SH1 to SH5 and SV1 to SV5 are temperature detection elements whose resistance value increases as the temperature of the linear thermistors SH1 to SH5 and SV1 to SV5 increases. In addition, the linear thermistors SH1 to SH5 extending in the x-axis direction and the linear thermistors SV1 to SV5 extending in the y-axis direction in the drawing are insulated from each other by an insulating layer provided therebetween. The linear thermistors SH1 to SH5 and SV1 to SV5 are processing circuits built in the temperature detection sheet 30 via lands LH11 to LH15, LH21 to LH25, LV11 to LV15, and LV21 to L25 formed at both ends. (Not shown) is electrically connected. The outer edge of the temperature detection sheet 30 is provided with a thermistor (not shown) having resistance temperature characteristics in accordance with the linear thermistors SH1 to SH5 and SV1 to SV5 as a part for detecting the ambient temperature (room temperature). It has been. In the present embodiment, as described above, the temperature detection sheet 30 formed in a sheet shape is used as the temperature detection unit including the linear thermistors SH1 to SH5, SV1 to SV5, processing circuits thereof, and the like. Thereby, since the temperature detection sheet 30 can be easily affixed to the upper surface of the primary coil L1, the attachment is easy.

  On the other hand, as shown in FIG. 1, the portable device 1 includes a secondary coil module 11 that receives power transmitted from the charger 2. The portable device 1 has a structure in which the outer periphery of various electronic components including the secondary coil module 11 and the secondary battery 10 is covered with a housing 12 to protect them from the external environment.

  The secondary coil module 11 includes a secondary coil L2 that generates a current by interlinking with the magnetic flux generated from the primary coil L1, and a ferrite member that suppresses leakage of the magnetic flux from the secondary coil L2. It is comprised with the magnetic body M2. As the secondary coil L2, a planar coil is used similarly to the primary coil L1. In the present embodiment, the number of turns of the secondary coil L2 is set to 15 turns, and the outer diameter thereof is set to 35 [mm]. The total thickness of the secondary coil L2 and the magnetic body M2 is set to about 0.5 [mm].

Next, the circuit configuration of the non-contact power transmission system of this embodiment will be described in detail with reference to FIG.
As shown in FIG. 3, the charger 2 includes a primary-side LC circuit 22 in which a resonance capacitor C1 is connected in parallel to a primary coil L1. The primary side LC circuit 22 constitutes a series circuit in which switching elements FET1 made of N-channel MOS transistors are connected in series. This series circuit includes, for example, a DC power supply E1 having a power supply voltage of 5 [V] and a capacitor. C2 is connected in parallel. The switching element FET1 is driven to be turned on / off by applying a control voltage (gate voltage) from a primary side control unit 23 mainly composed of a microcomputer. Then, when the switching element FET1 is turned on / off according to the gate voltage from the primary side control unit 23, alternating power is induced in the primary coil L1 by the DC power constantly supplied from the power source E1. That is, in this embodiment, the primary side control part 23 is a power transmission control means for controlling the supply of alternating power to the primary coil L1. Note that the oscillation frequency of the alternating power oscillated from the primary coil L1 through on / off of the switching element FET1 is about 100 kHz.

  On the other hand, the portable device 1 includes a half-wave rectifier circuit in which a diode D1 is connected in series to the secondary coil L2. That is, the alternating power received by the secondary coil L2 is converted into DC power by being half-wave rectified through the diode D1, and the converted DC power is supplied (charged) to the secondary battery 10 as a load. The

  On the other hand, the temperature detection sheet 30 includes a series circuit in which resistors R1 to R11 are respectively connected in series to the linear thermistors SH1 to SH5, SV1 to SV5, and the thermistor SA. Each series circuit corresponding to the linear thermistors SH1 to SH5, SV1 to SV5 and the thermistor SA is connected to a DC power supply E2 having a power supply voltage of 3.3 [V], for example. The DC power supply E2 is taken from the charger 2. The power supply voltage of the DC power supply E2 is divided by the resistors of the linear thermistors SH1 to SH5, SV1 to SV5 and the resistors R1 to R10, and the respective potentials are connected to the microcomputer via the terminals A1 to A10. It is taken into the sensor control part 31 comprised in the center. Further, the power supply voltage of the DC power supply E2 is divided by the thermistor SA and the resistor R11, and the potential is taken into the sensor control unit 31 via the terminal A11. The sensor control unit 31 is communicably connected to the primary control unit 23 via an appropriate wiring 40 that electrically connects the temperature detection sheet 30 and the charger 2. That is, the sensor control unit 31 and the primary side control unit 23 can exchange various signals via the wiring 40.

  The sensor control unit 31 monitors the temperatures TH1 to TH5 and TV1 to TV5 of the linear thermistors SH1 to SH5 and SV1 to SV5 based on the potentials of the terminals A1 to A10, and detects the temperature based on the potential of the terminal A11. The ambient temperature TB around the seat 30 is monitored. The sensor control unit 31 has a nonvolatile memory 31a, and the relationship between the potentials of the terminals A1 to A10 and the temperatures of the linear thermistors SH1 to SH5, SV1 to SV5 is shown in FIG. Is stored as a map as shown in FIG. The sensor control unit 31 calculates the temperatures of the linear thermistors SH1 to SH5 and SV1 to SV5 from the potentials of the terminals A1 to A10 with reference to the map shown in FIG. The non-volatile memory 31a of the sensor control unit 31 also stores a map (not shown) indicating the relationship between the potential of the terminal A11 and the environmental temperature TB. The sensor control unit 31 uses this map, The ambient temperature TB is map-calculated from the potential of the terminal A11. Then, by comparing the temperature of the linear thermistors SH <b> 1 to SH <b> 5, SV <b> 1 to SV <b> 5 with the environmental temperature TB, it is determined whether or not abnormal heating has occurred in the temperature detection sheet 30. When abnormal heating of the temperature detection sheet 30 is detected, an abnormality detection signal indicating that is transmitted to the primary side control unit 23 via the wiring 40. Thus, in the present embodiment, the sensor control unit 31 is an abnormality detection unit that detects abnormal heating of the temperature detection sheet 30. On the other hand, when the abnormality detection signal is transmitted from the sensor control unit 31, the primary side control unit 23 stops the on / off switching of the switching element FET1, thereby supplying the alternating power to the primary coil L1. Stop.

  Next, a process for detecting abnormal heating of the temperature detection sheet 30 executed through the sensor control unit 31 will be described in detail with reference to FIG. Note that the process shown in FIG. 5 is repeatedly executed with a predetermined calculation cycle during a period in which the alternating power is supplied to the primary coil L1.

  As shown in FIG. 5, in this process, first, the temperature of all linear thermistors SH1 to SH5, SV1 to SV5 is calculated from the potentials of the terminals A1 to A10 by map calculation using the map illustrated in FIG. TH1 to TH5, TV1 to TV5 are respectively detected (step S1). Similarly, the ambient temperature TB is detected from the potential of the terminal A11 by map calculation (step S2). In the subsequent step S3, temperature difference values ΔTH1 to ΔTH5, ΔTV1 to ΔTV5 obtained by subtracting the environmental temperature TB from the temperatures TH1 to TH5 and TV1 to TV5 of the linear thermistors SH1 to SH5 and SV1 to SV5 are calculated. . Further, it is determined whether any of the calculated temperature difference values ΔTH1 to ΔTH5, ΔTV1 to ΔTV5 is equal to or greater than a predetermined value Ta (step S4). The predetermined value Ta is obtained through a prior experiment or the like as a value that can detect the abnormal heat generation of the metal foreign matter described above. Here, when all of the temperature difference values ΔTH1 to ΔTH5 and ΔTV1 to ΔTV5 are smaller than the predetermined value Ta (step S4: NO), the sensor control unit 31 once ends this series of processes.

  On the other hand, if any of the temperature difference values ΔTH1 to ΔTH5 and ΔTV1 to ΔTV5 is equal to or greater than the predetermined value Ta (step S4: YES), it is determined that abnormal heating has occurred in the temperature detection sheet 30, and abnormal A detection signal is transmitted to the primary side control part 23 (step S5). That is, in this case, the supply of alternating power to the primary coil L1 is stopped by the primary side control unit 23.

  Next, an operation example (action) of the non-contact power transmission system according to the present embodiment will be described with reference to FIGS. Here, it is assumed that the ambient temperature TB around the charger 2 is 25 [° C.]. Further, it is assumed that the predetermined value Ta is set to 10 [° C.].

  For example, when charging of the portable device 1 from the charger 2 shown in FIG. 1 is started, a metal foreign object is placed on the upper surface 21a of the housing 21 of the charger 2 above the primary coil L1. Suppose you were. At this time, when the metal foreign object generates heat, the temperature detection sheet 30 is heated by the heat. Here, in this embodiment, as shown in the previous FIG. 2, since the linear thermistors are arranged in a lattice pattern on the temperature detection sheet 30, compared with the case where the temperature sensors are respectively arranged at a plurality of measurement points. The number of temperature detection elements can be reduced while ensuring a wide temperature detection range. For this reason, the structure of the temperature detection sheet 30 can be simplified. If the part A indicated by the two-dot chain line in the figure of the temperature detection sheet 30 is strongly heated by the heat generation of the metal foreign matter, the temperature of the linear thermistor SV4 positioned at the part A is, for example, 25 [ [° C.] to 40 [° C.].

  On the other hand, as shown in FIG. 3, the sensor controller 31 monitors the temperature of the linear thermistor SV4 and the environmental temperature TB based on the potentials of the terminals A7 and A11. When the temperature of the linear thermistor SV4 rises to 40 [° C.], the sensor control unit indicates that the temperature difference value obtained by subtracting the environmental temperature TB (25 [° C.]) from the temperature is larger than the predetermined value Ta. When detected by 31, an abnormality detection signal is transmitted to the primary side control unit 23. Thereby, since supply of the alternating power to the primary coil L1 is stopped, abnormal heat generation of the metal foreign object is suppressed.

  According to such a configuration as the temperature detection sheet 30, it is only necessary to transmit an abnormality detection signal from the temperature detection sheet 30 to the primary side control unit 23. Therefore, as shown in FIG. It is only necessary to connect the device 2 with the wiring 40. Thereby, since the communication structure between the temperature detection sheet 30 and the charger 2 can be extremely simplified, the structure as a non-contact power transmission system can be simplified while the heat generation of the metal foreign object can be detected. It becomes possible to plan.

As described above, according to the non-contact power transmission system according to the present embodiment, the following effects can be obtained.
(1) The temperature detection sheet 30 is provided with linear thermistors SH1 to SH5 and SV1 to SV5. The temperature detection sheet 30 is provided with a sensor control unit 31 that detects abnormal heating of the temperature detection sheet 30 based on temperatures detected through the linear thermistors SH1 to SH5 and SV1 to SV5. Then, when abnormal heating of the temperature detection sheet 30 is detected by the sensor control unit 31, the supply of alternating power to the primary coil L1 is stopped. Thereby, while ensuring the wide temperature detection range, while the number of temperature detection elements can be reduced, the communication structure between the temperature detection sheet | seat 30 and the charger 2 can also be simplified very much. Therefore, it is possible to simplify the configuration of the non-contact power transmission system while making it possible to detect the heat generation of the metal foreign object.

  (2) The temperature detection sheet 30 formed in a sheet shape is used as the temperature detection unit including the linear thermistors SH1 to SH5, SV1 to SV5, the sensor control unit 31, and the like. Thereby, since the temperature detection part can be easily affixed on the upper surface of the primary coil L1, the attachment becomes easy.

  (3) In the temperature detection sheet 30, the linear thermistors SH1 to SH5 and SV1 to SV5 are arranged in a grid pattern. Thereby, the temperature of the temperature detection sheet 30 can be detected more accurately.

  (4) The temperature detection sheet 30 is attached to the primary coil L1. Thereby, since electrical connection with the temperature detection sheet | seat 30 and the charger 2 can be performed easily, attachment of the temperature detection sheet | seat 30 becomes easy.

<Second Embodiment>
Next, 2nd Embodiment of the non-contact electric power transmission system concerning this invention is described with reference to FIGS. The second embodiment differs from the first embodiment in that the temperature detection sheet 30 is provided on the portable device 1 side. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and the same elements as those in the first embodiment will be denoted by the same reference numerals, and redundant description will be omitted. First, a schematic configuration of the non-contact power transmission system according to the present embodiment will be described with reference to FIG.

As shown in FIG. 6, in the present embodiment, the temperature detection sheet 30 is attached to the end surface of the secondary coil L2 opposite to the end surface in contact with the magnetic body M2 with an adhesive or the like.
Next, the circuit configuration of the non-contact power transmission system of this embodiment will be described in detail with reference to FIG. Since the circuit configuration of the temperature detection sheet 30 is the same as the configuration illustrated in FIG. 3, the illustration is omitted here for convenience.

  As shown in FIG. 7, in the charger 2, the primary side control unit 23 applies a gate voltage to the switching element FET1 via the gate resistor R20, so that the on / off control of the switching element FET1 is performed. Further, the primary side control unit 23 includes a terminal B1 connected to a connection point N1 between the primary side LC circuit 22 and the switching element FET1 via a diode D2. That is, the power at the connection point N1 is half-wave rectified and input to the terminal B1, and the primary side control unit 23 receives the alternating power voltage generated by the oscillation of the primary coil L1 through the terminal B1. The maximum voltage and the like can be acquired from the waveform.

  On the other hand, the portable device 1 includes a switching element FET2 that switches between supply and non-supply of the DC power rectified via the diode D1 to the secondary battery 10. The switching element FET2 is composed of a P-channel MOS transistor, and is turned on / off when a gate voltage is applied via a gate resistor R21 from a secondary-side control unit 13 mainly composed of a microcomputer. The A resistor R22 is provided between the drain and source of the switching element FET2. In addition, the portable device 1 includes a load adjustment circuit 14 connected in parallel to a series circuit constituted by the secondary coil L2 and the diode D1. The load adjustment circuit 14 is configured as a circuit in which a resistor R23 and a switching element FET3 composed of an N-channel MOS transistor are connected in series. The resistance value of the resistor R23 is set to about 47 [mΩ]. Further, the switching element FET3 is driven to be turned on / off when a gate voltage is applied from the secondary side control unit 13 via the gate resistor R24. In the present embodiment, the switching element FET3 is turned on / off while the switching element FET2 is turned off by the secondary side control unit 13, thereby causing the resistor R23 to be a load on the secondary coil L2. , It is switched to a state that does not become a load. As a result, the amplitude of the alternating power received by the secondary coil L2 is changed (modulated). That is, the power reception characteristic of the secondary coil L2 with respect to the power supplied by the primary coil is changed.

  By the way, the change in the power reception characteristics of the secondary coil L2 not only changes the amplitude of the power waveform of the alternating power received by the secondary coil L2, but also the primary coil L1 magnetically coupled to the secondary coil L2. The amplitude of the power waveform of the alternating power is also changed. That is, the amplitude of the power waveform (voltage waveform) of the alternating power induced in the primary coil L1 also changes in accordance with the change in the amplitude of the power waveform (voltage waveform) of the alternating power in the secondary coil L2. As a result, a change occurs in the amplitude (maximum voltage value) of the voltage waveform of the alternating power generated at the connection point N1 of the charger 2.

  On the other hand, a temperature detection sheet 30 is connected to the secondary side control unit 13 via an appropriate wiring 41. That is, the secondary side control unit 13 receives the abnormality detection signal transmitted from the temperature detection sheet 30 via the wiring 41. And the secondary side control part 13 supplies electric power to the secondary battery 10 by maintaining the switching element FET2 in the ON state during the period when the alternating power is transmitted from the charger 2. When an abnormality detection signal is received during this period, the switching element FET3 is turned on / off while the switching element FET2 is turned off and the state is maintained. Thus, the amplitude of the alternating power transmitted by the primary coil L1 is changed (modulated) in accordance with the abnormality detection signal by changing the amplitude of the alternating power received by the secondary coil L2. Thus, in the mobile device 1, the secondary side control unit 13, the switching element FET3, and the resistor R23 constitute a wireless communication unit for performing wireless communication with the charger 2.

Next, the modulation mode of the amplitude of the alternating power received by the secondary coil L2 by the secondary side control unit 13 will be described with reference to FIG.
For example, it is assumed that the secondary side control unit 13 performs on / off switching of the switching element FET3 based on the abnormality detection signal in the mode shown in FIG. At this time, in the period T1 in which the switching element FET3 is turned off, the amplitude of the alternating power received by the secondary coil L2 changes based on the amplitude A1a, as shown in FIG. 8B. Moreover, as shown in FIG.8 (c), the amplitude of the alternating power which the primary coil L1 transmits changes based on amplitude A2a. As a result, as shown in FIG. 8D, the voltage value of the DC power induced in the primary coil L1 and half-wave rectified by the diode D2 becomes the voltage Va. And in the primary side control part 23 by which this direct-current power is taken in via terminal B1, the information transmitted from the charger 2 is based on the judgment whether the voltage Va of terminal B1 exceeded the predetermined threshold value V0. It is determined whether the logic level is “H” or logic level “L”. That is, in the period T1, it is determined that the information transmitted from the secondary side control unit 13 to the primary side control unit 23 is the logic level “H”. Note that the threshold value V0 is set in advance through experiments or the like as a value that can determine a change in the amplitude of the alternating power induced in the primary coil L1.

  On the other hand, in the period T2 in which the switching element FET3 is on, as shown in FIG. 8B, the amplitude of the alternating power received by the secondary coil L2 decreases from the amplitude A1a to the amplitude A1b. Moreover, as shown in FIG.8 (c), the amplitude of the alternating power which the primary coil L1 transmits falls to amplitude A2b lower than amplitude A2a. As a result, as shown in FIG. 8D, the voltage value of the DC power induced in the primary coil L1 and half-wave rectified by the diode D2 also changes from the voltage Va to the voltage Vb. Since the voltage Vb is lower than the threshold value V0, the primary control unit 23 determines that the information transmitted from the secondary control unit 13 in the period T2 is the logic level “L”.

  And the primary side control part 23 demodulates the abnormality detection signal transmitted from the secondary side control part 13 based on such a method. When the abnormality detection signal is received, the supply of alternating power to the primary coil L1 is stopped by stopping the on / off switching of the switching element FET1.

  According to such a configuration as the non-contact power transmission system, when abnormal heating occurs in the temperature detection sheet 30, the fact is transmitted from the portable device 1 to the charger 2, and the power transmission of the charger 2 is performed. Can be stopped. Thereby, even when the temperature detection sheet 30 is provided on the portable device 1 side, it is possible to suppress abnormal heat generation of the metal foreign matter interposed between the charger 2 and the portable device 1. If the temperature detection sheet 30 can be provided on the portable device 1 side in this way, even if it is difficult to provide the temperature detection sheet 30 on the charger 2 due to structural restrictions, for example, contactlessness is possible. The temperature detection sheet 30 can be mounted on the power transmission system. For this reason, convenience comes to be improved.

  As described above, the non-contact power transmission system according to the present embodiment also provides the same effects as the effects (1) to (3) of the previous first embodiment, or effects equivalent thereto. In addition, the following effect can be obtained instead of the effect (4).

  (5) The temperature detection sheet 30 is provided on the portable device 1 side. When abnormal heating of the temperature detection sheet 30 is detected, the fact is transmitted from the temperature detection sheet 30 to the charger 2 via the portable device 1. Thereby, for example, even when it is difficult to provide the temperature detection sheet 30 in the charger 2 due to structural limitations, it is possible to suppress abnormal heat generation of the metal foreign matter through the temperature detection sheet 30 provided in the portable device 1. become able to.

<Third Embodiment>
Next, a third embodiment of the non-contact power transmission system according to the present invention will be described with reference to FIG. 9 and FIG. In addition, although this embodiment differs in the structure of the temperature detection sheet | seat 30 from previous 1st Embodiment, about another structure, it is the same as that of 1st Embodiment. Therefore, in this embodiment, the differences from the first embodiment will be mainly described, and the same elements as those in the first embodiment will be denoted by the same reference numerals, and redundant description will be omitted. First, the configuration of the temperature detection sheet 30 will be described with reference to FIG.

  As shown in FIG. 9, the temperature detection sheet 30 of the present embodiment includes a power receiving coil L3 that is linked to an alternating magnetic flux generated from the primary coil L1. The power receiving coil L3 is disposed in a region sandwiched between the linear thermistor SV1 and the linear thermistor SV3. The power receiving coil L3 is provided in a layer different from the layer on which the linear thermistors SH1 to SH5 and SV1 to SV5 are patterned, and is insulated from the linear thermistors SH1 to SH5 and SV1 to SV5. The temperature detection sheet 30 of this embodiment uses the alternating power induced in the power receiving coil L3 as the power supply voltage when the alternating magnetic flux generated from the primary coil L1 is linked to the power receiving coil L3.

Next, a circuit configuration of the temperature detection sheet 30 will be described with reference to FIG.
As shown in FIG. 10, in the temperature detection sheet 30, the alternating power induced in the power receiving coil L3 is rectified through a rectifier circuit 32 including a diode D3 and a capacitor C3 to be converted into DC power. Further, the DC power converted through the rectifier circuit 32 is stabilized to, for example, the power supply voltage 3.3 [V] through the regulator 33 and supplied to the sensor control unit 31 and the like.

  Thus, in this embodiment, since the alternating magnetic flux generated from the primary coil L1 links the power receiving coil L3, the alternating power induced in the power receiving coil L3 is used as the power source of the temperature detection sheet 30. There is no need to provide power supply wiring on the temperature detection sheet 30. For this reason, the wiring structure of the temperature detection sheet 30 can be simplified.

  As described above, the non-contact power transmission system according to the present embodiment also provides the same effects as the effects (1) to (4) of the previous first embodiment, or effects equivalent thereto. In addition, the following effects can be obtained.

  (6) The temperature detection sheet 30 is provided with the power receiving coil L3 interlinked with the alternating magnetic flux generated from the primary coil L1. Then, the alternating power induced in the power receiving coil L <b> 3 by the linkage of the alternating magnetic flux is used as the power source for the temperature detection sheet 30. Thereby, since it is not necessary to provide power supply wiring in the temperature detection sheet 30, the wiring structure of the temperature detection sheet 30 can be simplified.

<Fourth Embodiment>
Next, a fourth embodiment of the non-contact power transmission system according to the present invention will be described with reference to FIG. 11 and FIG. In addition, although this embodiment differs in the circuit structure of the temperature detection sheet | seat 30 and the charger 2 from previous 3rd Embodiment, about another structure, it is the same as that of 3rd Embodiment. Therefore, in the present embodiment, differences from the third embodiment will be mainly described, and the same elements as those in the third embodiment will be denoted by the same reference numerals, and redundant description will be omitted. First, the circuit configuration of the temperature detection sheet 30 will be described with reference to FIG.

  As shown in FIG. 11, the temperature detection sheet 30 has a sufficiently high frequency (for example, 1 [MHz]) compared to the oscillation frequency (100 [kHz]) of the alternating power induced in the primary coil L1. A Colpitts oscillation circuit 34 for oscillating radio waves is provided. Further, the temperature detection sheet 30 includes a switching element SW <b> 1 that interrupts the power feeding path of the Colpitts oscillation circuit 34. The switching / switching of the switching element SW <b> 1 is controlled by the sensor control unit 31, so that driving / stopping of the Colpitts oscillation circuit 34 is switched. Specifically, the sensor control unit 31 normally stops the oscillation of the radio wave from the Colpitts oscillation circuit 34 by maintaining the switching element SW1 in the off state. Further, the sensor control unit 31 oscillates a radio wave from the Colpitts oscillation circuit 34 by performing a process of turning on the switching element SW1 instead of the process of transmitting the abnormality detection signal. That is, in this temperature detection sheet 30, when abnormal heating of the linear thermistors SH1 to SH5 and SV1 to SV5 is detected, radio waves are oscillated.

  On the other hand, as shown in FIG. 12, the charger 2 includes a resonance circuit 25 including a coil L4 and a resonance capacitor C4 as a part for receiving a radio wave oscillated from the Colpitts oscillation circuit. The voltage generated in the resonance circuit 25 when receiving the radio wave is rectified and smoothed by the rectifier circuit 26 including the diode D4 and the capacitor C5, and is taken into the primary side control unit 23 via the terminal B2. . That is, when the radio wave oscillated from the Colpitts oscillation circuit 34 is received via the resonance circuit 25, the potential of the terminal B2 indicates a predetermined voltage value. And the primary side control part 23 determines whether the radio wave transmitted from the temperature detection sheet | seat 30 was received based on the determination whether the electric potential of terminal B2 exceeded the predetermined threshold value. The predetermined threshold is set through a preliminary experiment or the like as a value that can determine whether or not the radio wave oscillated from the Colpitts oscillation circuit 34 is received. And when it determines with having received the radio wave transmitted from the temperature detection sheet | seat 30, supply of the alternating power to the primary coil L1 is stopped by stopping switching of ON / OFF of switching element FET1. .

  As described above, in this embodiment, since the abnormality notification from the temperature detection sheet 30 to the charger 2 is performed wirelessly, it is necessary to provide communication wiring between the temperature detection sheet 30 and the charger 2. There is no. For this reason, the structure as a non-contact electric power transmission system can be simplified.

  As described above, the contactless power transmission system according to the present embodiment also has the same effects as the effects (1) to (4) and (6) of the previous first and third embodiments, or this effect. The following effects can be obtained.

  (7) The sensor control unit 31 provided in the temperature detection sheet 30 and the primary side control unit 23 provided in the charger 2 are connected so as to be capable of wireless communication. Thereby, since it is not necessary to provide the wiring for communication between the temperature detection sheet | seat 30 and the charger 2, the structure as a non-contact electric power transmission system can be simplified.

<Fifth Embodiment>
Next, a fifth embodiment of the non-contact power transmission system according to the present invention will be described with reference to FIGS. In the present embodiment, differences from the third embodiment will be mainly described, and the same elements as those in the third embodiment will be denoted by the same reference numerals, and redundant description will be omitted. First, the schematic configuration of the non-contact power transmission system will be described with reference to FIG.

  As shown in FIG. 13, in the present embodiment, the temperature detection sheet 30 is attached to a portion of the upper surface 21 a of the housing 21 of the charger 2 that is above the primary coil L <b> 1 with an adhesive or the like.

Next, with reference to FIG. 14, the structure of the temperature detection sheet | seat 30 of this embodiment is demonstrated.
As shown in FIG. 14, the temperature detection sheet 30 of this embodiment includes a magnetic coupling coil L5 that is magnetically coupled to the primary coil L1. The magnetic coupling coil L5 is disposed along the outer edge of the temperature detection sheet 30. The magnetic coupling coil L5 is provided in a layer different from the layer on which the linear thermistors SH1 to SH5 and SV1 to SV5 are patterned, and is insulated from the linear thermistors SH1 to SH5 and SV1 to SV5. .

Next, the circuit configuration of the temperature detection sheet 30 will be described with reference to FIG.
As shown in FIG. 15, the magnetic coupling coil L5 has one end connected to the ground line and the other end connected to the ground line via the switching element SW2. Then, the switching of the switching element SW2 on / off is controlled by the sensor control unit 31, whereby the short circuit to the ground line of the magnetic coupling coil L5 and the cancellation of the short circuit are performed. Specifically, the sensor control unit 31 normally releases the short circuit of the magnetic coupling coil L5 by keeping the switching element SW2 off. The sensor control unit 31 short-circuits the magnetic coupling coil L5 to the ground line by performing a process of turning on the switching element SW2 instead of the process of transmitting the abnormality detection signal. As a result, the magnetic coupling coil L5 becomes an obstacle and the magnetic coupling between the primary coil L1 and the secondary coil L2 is weakened, so the alternating power transmitted from the primary coil L1 to the secondary coil L2 is reduced. To do. At this time, the amplitude of the alternating power induced in the primary coil L1 and the secondary coil L2 changes as shown in FIG. 16, for example. That is, if switching of the switching element SW2 is performed as shown in FIG. 16C, the amplitude of the alternating power induced in the secondary coil L2 when the switching element SW2 is turned on is shown in FIG. As shown in FIG. 4, the amplitude decreases from the amplitude A3a to the amplitude A3b. On the other hand, the amplitude of the alternating power induced in the primary coil L1 increases from the amplitude A4a to the amplitude A4b as shown in FIG.

Next, the circuit configuration of the charger 2 will be described with reference to FIG.
As shown in FIG. 17, the primary side control unit 23 includes a terminal B3 to which a potential between the drain and the ground of the switching element SW1 is applied. The primary side control unit 23 monitors the amplitude of the alternating power induced in the primary coil L1 by monitoring the potential of the terminal B3. When it is detected that the amplitude of the alternating power induced in the primary coil L1 has changed from the amplitude A4a to the amplitude A4b as illustrated in FIG. 16B, abnormal heating is performed in the temperature detection sheet 30. Is determined to be detected. In this case, the primary side control unit 23 stops the supply of alternating power to the primary coil L1 by stopping the on / off switching of the switching element FET1.

  According to such a configuration as the non-contact power transmission system, the abnormality is notified from the temperature detection sheet 30 to the charger 2 without providing a communication wiring between the temperature detection sheet 30 and the charger 2. Can do. For this reason, the structure as a non-contact electric power transmission system can be simplified.

  On the other hand, in such a non-contact power transmission system, metal foreign objects are often placed on the upper surface 21 a of the housing 21 of the charger 2. Therefore, if the temperature detection sheet 30 is affixed to the upper surface 21a of the housing 21 of the charger 2, it becomes easier to detect the heat generation of the metal foreign object placed on the upper surface 21a of the housing 21, and consequently abnormal heat generation of the metal foreign object. It becomes possible to suppress more accurately.

  As described above, even with the non-contact power transmission system according to the present embodiment, effects equivalent to the effects (1) to (4) and (6) according to the first and third embodiments described above, or In addition to the effects similar to this, the following effects can be obtained.

  (8) The temperature detection sheet 30 is provided with a magnetic coupling coil L5 that is magnetically coupled to the primary coil L1 and that can be short-circuited at both ends via the switching element SW2. Moreover, in the sensor control part 31, when the abnormal heating of the temperature detection sheet | seat 30 is detected, the switching element SW2 is turned on and the magnetic coupling coil L5 is short-circuited, whereby the amplitude of the alternating power induced in the primary coil L1 is increased. It was decided to change. Furthermore, in the primary side control part 23, it decided to detect the abnormal heating of the temperature detection sheet | seat 30 based on the change of the amplitude of the alternating power induced by the primary coil L1. Thereby, since it is not necessary to provide the wiring for communication between the temperature detection sheet | seat 30 and the charger 2, the structure as a non-contact electric power transmission system can be simplified.

  (9) The temperature detection sheet 30 is attached to the upper surface 21 a of the housing 21 of the charger 2. Thereby, it becomes easy to detect the heat generation of the metal foreign object, and as a result, the abnormal heat generation of the metal foreign object can be more accurately suppressed.

<Other embodiments>
In addition, each said embodiment can also be implemented with the following forms which changed this suitably.
In the second embodiment, the abnormality detection signal is wirelessly transmitted from the secondary control unit 13 to the primary control unit 23 by modulating the amplitude of the alternating power induced in the secondary coil L2. . Instead of this, for example, when the mobile device 1 and the charger 2 are equipped with a wireless communication device (wireless communication means) for performing wireless communication between them, the wireless communication device 2 is used. An abnormality detection signal may be transmitted from the secondary control unit 13 to the primary control unit 23. In addition, when such a wireless communication device is not mounted on the mobile device 1 and the charger 2, it may be newly mounted on the mobile device 1 and the charger 2.

  In the third embodiment, the power receiving coil L3 is disposed in the region sandwiched between the linear thermistor SV1 and the linear thermistor SV3 of the temperature detection sheet 30, but the shape and the layout of the power receiving coil L3 Can be appropriately changed.

  In the fourth embodiment, the Colpitts oscillation circuit 34 is used to perform wireless communication between the temperature detection sheet 30 and the charger 2. However, for wireless communication between these, appropriate wireless communication is performed. The thing using an apparatus can be employ | adopted.

  In the fourth embodiment, the wireless communication unit that receives the radio wave transmitted from the temperature detection sheet 30 is provided in the charger 2. However, the wireless communication unit may be provided in the portable device 1. Such a configuration is particularly effective when the temperature detection sheet 30 is attached to the surface of the portable device 1 in the second embodiment described with reference to FIGS. That is, by adopting such a configuration, the sensor control unit 31 of the temperature detection sheet 30 and the secondary side control unit 13 of the portable device 1 illustrated in FIG. There is no need to provide a wiring structure for communication between the temperature detection sheet 30 and the portable device 1. For this reason, the structure as a non-contact electric power transmission system can be simplified.

  In the fifth embodiment, the temperature detection sheet 30 is attached to the surface of the housing 21 of the charger 2, but instead, it may be attached to the surface of the housing 12 of the portable device 1. In this case, for example, as shown by a two-dot chain line in FIG. 7, the secondary side control unit 13 is provided with a terminal B4 to which a voltage induced in the secondary coil L2 is applied. And the secondary side control part 13 monitors the amplitude of the alternating power induced by the secondary coil L2 by monitoring the electric potential of terminal B4. Further, when it is detected that the amplitude of the alternating power induced in the secondary coil L2 has changed to the amplitude A3b, it is determined that abnormal heating has occurred in the temperature detection sheet 30. In this case, the secondary side control unit 13 detects abnormal heating in the temperature detection sheet 30 by changing the amplitude of the alternating power induced in the secondary coil L2 as needed through switching of the switching element FET3. This is notified to the primary side control unit 23. According to such a configuration, the temperature detection sheet 30 can be attached to the surface of the housing 12 of the mobile device 1. For this reason, even if it is difficult to attach the temperature detection sheet 30 to the surface of the charger 2 due to structural restrictions, for example, the heat generation of the metal foreign matter is suppressed through the temperature detection sheet 30 provided in the portable device 1. Will be able to.

  In each of the above embodiments, the linear thermistors SH1 to SH5 and SV1 to SV5 are arranged in a lattice pattern on the temperature detection sheet 30, but instead, for example, as shown in FIG. 18, a linear thermistor SH1 is used. ˜SH5 may be arranged side by side along only the y-axis direction in the drawing. According to such a configuration, the number of temperature detection elements can be reduced as compared with the case where the linear thermistors are arranged in a grid pattern, so that the cost can be reduced.

  In each of the above embodiments, the temperature detection unit including the linear thermistors SH1 to SH5, SV1 to SV5, the sensor control unit 31 and the like is formed in a sheet shape, but the temperature detection unit is formed in a box shape, for example. For example, the shape of the temperature detection unit may be changed as appropriate.

  In each of the above embodiments, the power receiving circuit unit including the primary coil L1 is mounted on the charger, and the power transmission circuit unit including the secondary coil L2 is mounted on the portable device. The mounting target of the power receiving circuit unit and the power transmitting circuit unit is not limited to these chargers and portable devices. In short, the present invention can be applied to any contactless power transmission system that receives the alternating power supplied to the primary coil via the secondary coil and supplies the received power to the load.

  L1 ... primary coil, L2 ... secondary coil, L3 ... power receiving coil, L5 ... magnetic coupling coil, SW2 ... switching element, SH1-SH5, SV1-SV5 ... linear thermistor (temperature detection element), 12, 21 ... housing , 14 ... Load adjustment circuit (wireless communication means), 30 ... Temperature detection sheet (temperature detection section), 31 ... Sensor control section (abnormality detection means), 23 ... Primary side control section (power transmission control means).

Claims (13)

The alternating magnetic flux generated from the primary coil by the supply of alternating power is linked to the secondary coil to receive the alternating power supplied to the primary coil via the secondary coil, and the received received power is loaded. A non-contact power transmission system for supplying to
A temperature detection unit provided between the primary coil and the secondary coil and provided with a temperature detection element extending linearly;
An abnormality detection means provided in the temperature detection unit for detecting abnormal heating of the temperature detection unit based on a temperature detected through the temperature detection element;
A non-contact power transmission system comprising: power transmission control means for stopping supply of alternating power to the primary coil based on detection of abnormal heating of the temperature detection unit through the abnormality detection means. The non-contact power transmission system according to claim 1, wherein the temperature detection unit is formed in a sheet shape. The non-contact power transmission system according to claim 1, wherein the temperature detection elements are arranged in a lattice pattern in the temperature detection unit. The temperature detection unit is provided with a power receiving coil interlinked with the alternating magnetic flux generated from the primary coil, and the temperature detection unit supplies alternating power induced in the power receiving coil by the interlinking of the alternating magnetic flux. The non-contact power transmission system according to any one of claims 1 to 3. The contactless power transmission system according to any one of claims 1 to 4, wherein the temperature detection unit is provided in the primary coil. The contactless power transmission system according to claim 1, wherein the temperature detection unit is provided on a surface of a housing that covers an outer periphery of the primary coil. The non-contact power transmission system according to claim 1, wherein the temperature detection unit is provided in the secondary coil. The contactless power transmission system according to claim 1, wherein the temperature detection unit is provided on a surface of a housing that covers an outer periphery of the secondary coil. The contactless power transmission system according to any one of claims 1 to 8, wherein the abnormality detection unit is connected to the power transmission control unit so as to be capable of wireless communication. The temperature detection unit includes a magnetic coupling coil that is magnetically coupled to the primary coil, and a switching element that short-circuits both ends of the magnetic coupling coil.
The abnormality detection means, when detecting abnormal heating of the temperature detection unit, changes the amplitude of the alternating power generated in the primary coil by short-circuiting both ends of the magnetic coupling coil through the switching element,
The non-contact power transmission system according to any one of claims 1 to 8, wherein the power transmission control unit detects abnormal heating of the temperature detection unit based on a change in amplitude of alternating power generated in the primary coil. . The device equipped with the secondary coil is provided with wireless communication means capable of performing wireless communication with the power transmission control means,
The abnormality detection means is communicably connected to the wireless communication means and, when detecting abnormal heating of the temperature detection unit, wirelessly transmits the fact to the power transmission control means via the wireless communication means. The contactless power transmission system according to 7 or 8. The non-contact power transmission system according to claim 11, wherein the abnormality detection unit is connected to the wireless communication unit so as to be capable of wireless communication. The temperature detection unit includes a magnetic coupling coil coupled to the secondary coil, and a switching element that short-circuits both ends of the magnetic coupling coil.
The abnormality detection means, when detecting abnormal heating of the temperature detection unit, changes the amplitude of the alternating power generated in the secondary coil by short-circuiting both ends of the magnetic coupling coil through the switching element,
The non-contact power transmission system according to claim 11, wherein the power transmission control unit detects abnormal heating of the temperature detection unit based on a change in amplitude of alternating power generated in the secondary coil.

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